Ducati Elettronica ignition trigger '72-'74 singles

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Bill48S
Cucciolo - the Lil Pup
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Ducati Elettronica ignition trigger '72-'74 singles

Post by Bill48S » Thu Nov 20, 2014 11:49 pm

Does anybody out there know the details of this inductor pickup?
I've depotted my non-working unit and find a coil of 47 ohms resistance, a 1N-series half-wave rectifier diode and a 330 ohm resistor wired in parallel to the coil.
I'm suspecting one or more shorted turns in the coil, as I'd expect closer to 500 ohms, also not real sure that the 330R is original (it's been "repaired" previously).
The Ducati factory don't seem inclined to reply to historic queries, so any info would be very much appreciated.

Ciao

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Craig in France
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Re: Ducati Elettronica ignition trigger '72-'74 singles

Post by Craig in France » Fri Nov 21, 2014 1:19 am

Hi Bill,

In 2008 I had a pick-up rebuilt by this company in the UK who might be able to advise, assuming they still have the details of what they found/did.

http://www.westcountrywindings.co.uk/

My contact was Michael Simmons.

P.s The other people who might be able to help is the Amici dello Scrambler. But Ducati itself won't have a clue :~ . As well as their general ignorance about much of their own history, Ducati Meccanica and Ducati Elettronica were already 2 separate companies by then.

P.p.s A similar looking DE pick-up was used on the Morini 3½. But whether they're similar inside electronically, I don't know.

HTH

Craig
Last edited by Craig in France on Sun Nov 23, 2014 3:36 am, edited 1 time in total.

Bill48S
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Re: Ducati Elettronica ignition trigger '72-'74 singles

Post by Bill48S » Fri Nov 21, 2014 12:34 pm

Thanks Craig - I'll check that link out :-)
Ultimately it's going to involve a total dismantling I guess, so I'll be able to measure the length of the winding, although I'd rather avoid that if possible lol

Bill

jockduck
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Re: Ducati Elettronica ignition trigger '72-'74 singles

Post by jockduck » Fri Jan 09, 2015 3:41 pm

The singles use the same red transducer box as the bevel twins? I assume there are two trigger coils, a static for starting and a full advance.
I unpicked a twin stator and this is what I got, retard trigger coil 652 turns 0.15mm wire 18.8 ohms, advance coil 330 turns 8.8 ohms, The charge pump coils were ok so I did not rewind them but they have a lot of turns and run to 280ohms.
Jock

Bill48S
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Re: Ducati Elettronica ignition trigger '72-'74 singles

Post by Bill48S » Thu Jan 29, 2015 3:37 am

From what I've gleaned from the 'net, there's only a single winding on the induction coil and the advance curve is generated by the rate of magnetic flux buildup relative to revs. I'm not an electronics engineer, so considering that Ducati in those years were pretty well versed in the KISS principle I'll go with that for the meantime.
On dissasembly, I tried to measure each fragment of wire I unravelled - with laquered assembly, not always a straight unwinding; sometimes short lengths came away in parallel, ect but the total of the very fine fragments in the bucket was over 30 metres. I'm guessing around 40, allowing for my hamfisted reverse engineering :-)

Using the specs for 0.1 mm copper wire, 40 metres should give around 85 ohms resistance through the coil itself.
When I dismantled my trigger there was a 330 ohm resistor connected in parallel to the coil, along with a 1N-series diode to ensure DC current to the transducer (or ignitor as the Jap brands call it).

Using the usual calcs, that should give a total resistance through the trigger unit of somewhere around 70 ohms. I vaguely remember a bit less than 100 when it was still working, but that was with a cheap meter and the dry joints etc that led to the eventual failure may have been there.

Next step is to rewind the bugger - tdious I'm sure :-)

machten
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Re: Ducati Elettronica ignition trigger '72-'74 singles

Post by machten » Fri Jan 30, 2015 7:10 am

I have a 450 Ducati Electronica CDI system that was working when I removed it. The ignition was fine, I replaced it with an Electrex system due to Stator battery charging issues, the ignition was fine. Are there some measurements I can take for you?

Kev

Bill48S
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Re: Ducati Elettronica ignition trigger '72-'74 singles

Post by Bill48S » Fri Jan 30, 2015 1:29 pm

Thanks Kev, that would be great!
If you could just measure the resistance across the output leads it's a simple calculation after that. It'll appear open circuit in one direction,due to the diode but we expect that.

Cheers,
Bill

machten
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Re: Ducati Elettronica ignition trigger '72-'74 singles

Post by machten » Sun Feb 01, 2015 5:43 am

Hi Bill,

Based on what you've found by unpotting the pickup, this doesn't seem to make sense...

Here's my pickup unit...

Image

Resistance one way on 20 MOhm test....open circuit...

Image

The other way..5+ megaOhms on a 20 MOhm test...

Image

I tested it with another gauge...same result. I didn't change it myself, so it is possible it wasn't working, but I'm pretty sure it was.

Kev

Bill48S
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Re: Ducati Elettronica ignition trigger '72-'74 singles

Post by Bill48S » Mon Feb 02, 2015 3:20 am

Thanks Kev - you're right, that's a really strange result. Puzzling.
Thinking back, when my unit had definitely failed there were sometimes "ballpark" resistance readings going open circuit within about a second and sometimes several megohms. Initially I thought maybe a capacitor somewhere in the mix, but on depotting certainly not.

I'm starting to suspect the first problem may have been due to shorted turns in the winding, then the "professional repair" may have made it worse by introducing a dry joint or two. And maybe the repairer's repotting resin may have been slightly conductive? No way of telling on that, 'cos it's all in the bin long ago :-)

I've just assembled the basic framework for a manually powered rewinding machine, so with a bit of luck might get to start rebuilding the coil next week (race meeting on this coming weekend, so not much work will get done).

The plan is to wind enough on to fill the armature, then check the output voltage with the diode installed and adjust the parallel resistor's value to deliver 0.7VDC or so. The aftermarket thyristor I'm using works on a gate voltage of 0.5 - 1.2 (from memory). Watch this space, as they say :-)

Bill

Bill48S
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Re: Ducati Elettronica ignition trigger '72-'74 singles

Post by Bill48S » Mon Feb 02, 2015 3:25 am

Hi again Kev,
'Scuse me for asking, but what's the green wire connected to? It looks like a link wire of some sort with nothing on the other end?

Cheers,
Bill

machten
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Re: Ducati Elettronica ignition trigger '72-'74 singles

Post by machten » Mon Feb 02, 2015 6:28 pm

Hi Bill,

It's not clear in the pictures, but one of the wires from the pickup has two terminals on it, with the tail wire the short green one. I'd need to have a look at the wiring harness to trace where it's going. It's not exactly clear from the wiring diagram as there appears to be three wires on a common connection to the CDI/Coil unit.
Wiring Diagram - Scrambler Electronic Ignition.jpg
Kev

machten
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Re: Ducati Elettronica ignition trigger '72-'74 singles

Post by machten » Tue Feb 03, 2015 4:55 am

Btw....I also saw when measuring a declining resistance from about 8MOhm before it stabilised which also looked like a capacitor in the circuit.

Kev

Bill48S
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Re: Ducati Elettronica ignition trigger '72-'74 singles

Post by Bill48S » Tue Feb 03, 2015 11:37 pm

Hi Kev - thanks for that, it's been so long since I've seen the "original" set-up I'd forgotten about the grounding wire on the negative lead from the trigger.
I gave away the road equipment on mine 20-odd years ago when I'd planned to make it a track bike, so connected that to a handlebar kill switch.
Now that she's back to road trim with an aftermarket headlamp , things are changing again :-) - including a Jaycar "transducer" as an alternative.

That "spike" and fade is a puzzlement though as there's definitely no capacitor there. Could the applied voltage from the multimeter be inducing an emf in the coil for a short time? As I've said, I'm no electronics engineer, so that's a total guess.

Cheers,
Bill

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